There has conventionally been a biosensor in which a sample is introduced into a cavity from a front-end sample supply port by a surfactant layer applied to an upper surface in the cavity. A sensor electrode is composed of a working electrode and a counter electrode, and an oxidation-reduction current value between the counter electrode and the working electrode is measured to determine the quantity of a target substance.
To be specific, many of the conventional biosensors are enzyme sensors using enzymes, and an enzyme sensor is configured such that a working electrode and a counter electrode are placed apart from each other with a predetermined interval and contacting a reduced electron carrier that is obtained by a specific reaction between the target substance and the enzyme, and a voltage is applied between the working electrode and the counter electrode for a predetermined period to oxidize the reduced electron carrier, and a current value (waveform) obtained at this time is measured to determine the quantity of the target substance.
Hereinafter, an example of a biosensor measurement system using an enzyme reaction will be described with reference to FIG. 7.
A biosensor measurement system 700 includes a biosensor 30 having a sample application part 30a at its front end, and a measurement device 10 which measures the concentration of a specific component in a liquid sample applied to the sample application part 30a. 
The measurement device 10 includes a support part 2 in which the biosensor 30 is inserted, and a display part 11 which displays the measurement result.
FIG. 8 shows an example of the biosensor 30, which is obtained by laminating a cover 31, a spacer 33, a reagent layer 35, and an insulating substrate 36.
The cover 31 has a vent hole 32 in its center.
The spacer 33 has an approximately rectangular sample supply channel 34.
The reagent layer 35 supports a reagent which enzymatically reacts with the specific component in the liquid sample.
The insulating substrate 36 comprises polyethylene terephthalate or the like, and an electrode layer is formed at its surface. The electrode layer is divided by laser or printing, thereby forming a working electrode 37, a detection electrode 38, and a counter electrode 39.
In the conventional biosensor, a disordered waveform is caused by an external factor such as an impact due to falling of the sensor during measurement, or a procedure of sample application, or a deterioration of the sensor itself due to such as exposure, resulting in abnormal values.
To be specific, in the above-described conventional biosensor, the quantity of electrons on the working electrode dramatically varies and thereby a higher value or a lower value relative to an appropriate response value might be shown in the following cases (1) to (4), resulting in a deterioration of the measurement precision.
(1) when the continuity of the suction of the sample into the cavity is interrupted while applying the sample to the sensor,
(2) when the sample is supplied through an unexpected part such as the vent hole,
(3) when the sample in the cavity is scattered, effused, or flowed out due to an external factor after starting the measurement,
(4) when the preservation state is poor (by such as exposure)
As described above, in the conventional biosensor, the reduced electron carrier substance which is obtained by a specific reaction between the target substance and the enzyme is oxidized by applying a voltage between the working electrode and the counter electrode for a predetermined period, and the obtained current value (waveform) is measured to determine the quantity of the target substance. However, since the conventional self monitoring blood-glucose biosensor comprising the sensor and the measurement device is very small in size, it might be dropped due to faulty operation or the like.
Further, in the biosensor, a disordered waveform (abnormal waveform) is caused by an external factor such as an impact due to falling of the sensor or a procedure of sample application during the measurement time, and thereby the measured value is significantly deviated from the true value.
The conventional biosensors as described above are disclosed in the following documents.
Patent Document 1: Japanese Published Patent Application No. 2004-245836
Patent Document 2: Japanese Published Patent Application No. 2003-4691
Patent Document 3: Japanese Published Patent Application No. Hei. 8-304340
Patent Document 4: International Publication WO 99/60391
Patent Document 5; National Publication of Translated Version No. 8-502589